Enneads III.6: Of the Impassibility of Incorporeal Entities (Soul and and Matter)
Matter as the Eternal Location or Residence of Generation
13. They would further have to explain in what sense they say that matter seeks to elude form. How can it be said to seek to elude the stones and the solid objects which contain it? For it would be irrational to say that it seeks to elude form at certain times, but not at others. If matter seeks to elude form voluntarily, why does it not elude form continuously? If necessity keep matter (within form), there can be no moment when it would not inhere in some form or other. The reason why matter is not always contained by the same form must not be sought for within matter, but in the forms that matter receives. In what sense then could it be said that matter eludes form? Does it always and essentially elude form? This would amount to saying that matter, never ceasing being itself, has form without ever having it. Otherwise, the statement would be meaningless.[69] (Plato) says that matter is the "nurse and residence of generation." If then matter be the nurse and residence of generation, it is evidently distinct from the latter. Only that which can be affected is within the domain of generation. Now as matter, being the nurse and residence of generation, exists before the latter, it must also exist before any alteration. Therefore to say that matter is the nurse and residence of generation is tantamount to saying that matter is impassible. The same meaning attaches to such other statements as that matter is that in which begotten things appear, and from which they issue,[70] that matter is the (eternal) location, and place (of all generation).[71]
When Plato, rightfully, calls matter "the location of forms," he is not thereby attributing any passion to matter; he only indicates that matters go on in a different manner. How? Since matter, however, by its nature, cannot be any of the beings, and as it must flee from the "being" of all beings, and be entirely different from them--for ("seminal) reasons" are genuine beings--it must necessarily preserve its nature by virtue of this very difference. It must not only contain all beings, but also not appropriate what is their image; for this is that by which matter differs from all beings. Otherwise, if the images that fill a mirror were not transient, and if the mirror remained invisible, evidently we would believe that the things the mirror presents to us existed really. If then there be something in a mirror, that is that which sense-forms are in matter. If in a mirror there be nothing but appearance, then there is nothing in matter but appearance, recognizing that this appearance is the cause of the existence of beings, an existence in which the things that exist always really participate, and in which the things which do not really exist do not participate; for they could not be in the condition where they would be if they existed without the existence of existence in itself.